Student Project Abstracts 2005 - Pluto - University of Washington

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QUINOXALINE-CONTAINING POLYFLUORENES: ENHANCED BLUE ELECTROLUMINESCENCE BY ADDITION OF A HOLE BLOCKING LAYERsol’n sol’n thin thinUV/Vis/Near-IR polymer spectrophotometer (nm) (nm) was used film to record film the absorptionspectrum. The PL emission was obtained (nm) using (nm) a PhotonTechnology QXF2 International 385 spectrofluorimeter 415 383 with an 438 excitationwavelength QXF5 of 380 nm for 382 all devices. 415 Table 3821 shows 437 all resultsfor absorption QXF15 and PL emission 377 spectra. 415 381 428aThe absorption maximum in toluene solution or inababa thin film. λ maxλ maxλ maxλ max b sol’n sol’n thin thinFigure 2. Device Configurations of (top left) ITO/PEDOT/QXF/LiF/The PL emission maximum in toluene solution orin polymer a thin film. (nm) (nm) film filmAl (Diode I), (top right) ITO/PEDOT/PVK/QXF/LiF/Al (Diode II),(nm) (nm)and (bottom) ITO/PEDOT/PVK/QXF/TPBI/LiF/Al (Diode III).QXF2 385 415 383 438Photophysical QXF5 382 properties 415 were 382 measured 437 insolid QXF15 state and 377 a solution 415 state. 381The solution 428aThe state absorption environment maximum afforded in toluene solution a study or of in a a thin single film.bThe polymer PL emission chain. maximum Conversely, in toluene solution the thin or in film a thin state film.allows insight into the how the polymer chainsinteract with Table one 1. Photophysical another. Properties Therefore, the thinfilm, or solid state, expresses the properties of aPhotophysical system of properties polymer were chains measured and in how solid state their and asolution state. interactions The solution effect emission state environment and absorption afforded of a studywavelengths of light.of a single polymer chain. Conversely, the thin film state allowsThe absorption spectra of both the thin filminsight intoandthesolutionhow thestatepolymerare shownchainsininteractFigurewith3a andone3b.another.Therefore, The the absorption thin film, or spectra solid show state, expresses the absorption the properties ofof a system energy of polymer as electrons chains and are how promoted their interactions to various effectemission vibronic and absorption levels of within wavelengths the excited of light. state andallows for the study of the ground state of theGlass coated with indium-tin oxide (ITO) was used as thesubstrate and anode. The ITO glass was cleaned by a processof twenty minute cycles of sonication in deionized (DI) water, a50:50 by volume mixture of DI water and isopropyl alcohol, toluene,DI water, and acetone, respectively. The substrate was driedovernight under vacuum. PEDOT was spin cast from a filtered1:3 dispersion of PEDOT and DI water. The PEDOT layer wasspin cast onto the ITO to achieve on average a thickness of 55nm. The PEDOT layer was heat treated at 180°C for ~15 minutesunder vacuum. Where applicable, a 10-15 nm layer of PVK wascast onto the PEDOT layer and dried four hours at 50°C undervacuum. The copolymer [QXF(2,5,15)] was cast subsequentlyfrom a filtered 1% weight solution in toluene to achieve a 50-60nm layer and was dried overnight under vacuum at 50°C. Whenapplicable, a 20-25 nm layer of TPBI was deposited via thermalevaporation at pressures of less than 3 x 10 -6 torr and a depositionrate of 0.2-0.3 nm/s.. The electrodes were also deposited usingthermal evaporation. 2 nm of LiF was evaporated followed by145-150 nm of Al deposited without breaking vacuum at pressures
max bthinfilm(nm)438437428ion or inution orured insolutionsinglelm stater chainsthe thinties of atheirtion ofIt is understood that increased conjugation lengthleads to red shifted absorption. Therefore, thehigher energy absorption band of the QXF15relative to QXF2 is indicative of decreasingconjugation length due to the increasingto the increasingquinoxalinequinoxalinecontent.content.The quinoxalineThe quinoxalinecontentcontentinterrupts interrupts the conjugation the conjugation along the carbon along backbone the carbon of the polymerby introducing backbone of kinks the and polymer bends which by introducing disturb the kinks delocalizedelectron and cloud. bends which disturb the delocalized electroncloud.Normalized Intensity1.210.80.60.40.20aThin Film PLE i i400 450 500 550 600Wavelength( )QXF2QXF5QXF15Solution State PL EmissionQXF2QXF5QXF15450 500 550 600Wavelength( )Figure 4. Photoluminescent Emission Emission Spectra of Spectra QXF2, ofin film QXF2, QXF5, QXF5, and QXF15 and QXF15 in (a) thin in film (a) and thin (b) film solution. and (b)and 3b. solution.tion ofThe PL The emission PL emission spectra for spectra both thin for both film and thin solution film statevarious and solution state are shown in Figure 4 withare shown in Figure 4 with maximum emission at 383 nm (QXF2)ate and maximum emission at 383 nm (QXF2) and 438of the and 438nmnm (QXF2),(QXF2),respectively.respectively.TheThePLPLemissionemissionisisa snapshotasorption excited state snapshot of the excited copolymer state and of emission the copolymer is a result and of the relaxationemission of excited is electrons a result of from the the relaxation lowest vibration of excited level ofQXF2the excited electrons state to from the ground the lowest state. vibration The solution level state of theQXF5PL emissionspectrum excited (Figure state to 4b) the is red ground shifted state. ~34 nm The from solution the solutionQXF15state PL emission spectrum (Figure 4b) is redstate absorption spectrum, and the thin film PL spectrum (Figureshifted ~34 nm from the solution state4a) is redabsorptionshifted ~50spectrum,from the thinandfilmtheabsorptionthin filmspectrum.PLThethin film spectrum PL emission (Figure spectra 4a) is shows red shifted a ~15 nm ~50 red from shift the relativeto the solution thin film state absorption emission. spectrum. The red The shift thin film the PL spectrasuggests emission increasing spectra conjugation shows length a ~15 as a nm result red of shift450 500interchaininteractions relative between to the neighboring solution state polymer emission. and increased The red delocalizationof electrons that resulted in a lower energyshift in the PL spectra suggests increasingQXF5,emission.bIRVINElectroluminescent PropertiesTable 2 shows the electroluminescent properties of Diodes I,II, and III (Figure 2) based on QXF2, QXF5, and QXF15 as theemissive layers. The results for the single layer (Diode I) deviceswill not be shown graphically or in tabular form. The electronicstructures for Diodes I, II, and II are shown in Figure 5. The valuesare of the electron affinity (EA) and ionization potential (IP)of each material. The electronic structures of each diode showthe extent of barrier to charge injection between adjacent layersand demonstrate the ease of charge mobility through the diode.QXF has a low-lying IP of 5.8 eV relative to vacuum level (0 eV).The addition of PEDOT as a hole injection layer between the anodeand the emissive layer minimized the barrier to hole injection,but a significant difference of 0.6 eV still existed between the IPsof PEDOT and QXF. PVK has an ionization potential of 5.8 eVthat approaches ohmic contact between the IP of QXF and the IPof PVK implying that no barrier for the injection of holes intothe emissive layer exists. Diode I was fabricated to insure thatDiode II was demonstrating enhanced device performance for allmolar ratios due to the minimization of the barrier to charge injection.Kulkarni, et al., completed the cyclic voltammetry of thecopolymer and found no significant differences in the ionizationpotential and electron affinity of the copolymer relative to PFO. 6However, it was expected that the addition of the n-type quinoxalinemoiety would improve the electron transport properties ofthe materials leading to a higher electron affinity. TPBI has alow- lying ionization potential at 6.7 eV that blocks holes andaides in confining charge recombination to the emissive layer.Therefore, the addition of the TPBI hole blocking layer could improveperformance and efficiency of the devices by minimizingquenching of the charges at the interfaces.L max(cd/m 2 )J L max(mA/cm 2 )V a(V)V onλ maxELEQE b%LE c(cd/A)L @ LE(cd/m 2 )CIE 1931(V) (nm)PVK DeviceQXF2 305 170 11 ~5 422 0.81 0.20 235 (0.16, 0.04)QXF5 1180 470 15 ~5 421 0.33 0.25 1180 (0.16, 0.04)QXF15 176 221 11 ~6 421 0.34 0.092 110 (0.16, 0.05)TPBI DeviceQXF2 1620 185 13 ~5 424 1.52 0.91 1530 (0.19, 0.09)QXF5 1510 265 12 ~5 437 1.77 0.71 115 (0.16, 0.05)QXF15 425 137 13 ~6 424 0.81 0.40 165 (0.15, 0.08)PFO 700 170 8 ~4 421 3.2 0.91 108 (0.16, 0.11)aDrive Voltage, b External Quantum Efficiency is defined as the ratio ofthe number of photons emitted per number of electrons injectedcLuminous Efficiency is a calculation made by dividing the maximumluminance (L max) but the current density at the L max.Table 2. Electroluminescent CharacteristicsCMDITR Review of Undergraduate Research Vol. 2 No. 1 Summer 2005 63
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The material is based upon work sup
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TABLE OF CONTENTSSynthesis of Dendr
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6 CMDITR Review of Undergraduate Re
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SYNTHESIS OF DENDRIMER BUILDING BLO
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throughout the work period. Five su
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Page 14 and 15: BARIUM TITANATE DOPED SOL-GEL FOR E
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Page 18 and 19: SYNTHESIS OF NORBORNENE MONOMER OF
Page 20: 20 CMDITR Review of Undergraduate R
Page 23 and 24: using different reaction conditions
Page 25 and 26: Synthesis of Nonlinear Optical-Acti
Page 27 and 28: quality of the XRD structures wasca
Page 29 and 30: Behavioral Properties of Colloidal
Page 32 and 33: Transmission electron microscopy ha
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Page 38 and 39: Fabry-Perot modulators with electro
Page 42 and 43: QUANTIZED HAMILTON DYNAMICS APPLIED
Page 46 and 47: INVESTIGATING NEW CLADDING AND CORE
Page 48 and 49: Dr. Robert NorwoodChris DeRoseAmir
Page 50 and 51: SYNTHESIS OF TPD-BASED COMPOUNDS FO
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Page 54 and 55: OPTIMIZING HYBRID WAVEGUIDESpropaga
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Page 58 and 59: SYNTHESIS AND ANALYSIS OF THIOL-STA
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Page 68 and 69: SYNTHESIS OF DENDRON-FUNCTIONALIZED
Page 72 and 73: BUILDING AN OPTICAL OXIMETER TO MEA
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CHARACTERIZATION OF THE PHOTODECOMP
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ELECTROLUMINESCENT PROPERTIES OF OR
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DETERMINATION OF MOLECULAR ORIENTAT
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DETERMINATION OF MOLECULAR ORIENTAT
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HYDROGEL MATERIALS FOR TWO-PHOTON M
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HYDROGEL MATERIALS FOR TWO-PHOTON M
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THE DESIGN OF A FLUID DELIVERY SYST
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Student Project Abstracts 2005 - Pluto - University of Washington

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